1. Field of the Invention
The present invention relates to a light scanning apparatus used with an image forming apparatus such as a laser beam printer, copying machine and the like, in which an image is formed or recorded by scanning the image with a laser beam.
2. Related Background Art
Conventionally, as a light scanning apparatus of this kind, a light scanning apparatus used with an image forming apparatus shown in FIG. 12 has been proposed. More particularly, a light scanning apparatus 205 is constituted by a laser source (not shown) for emitting a laser beam, a rotatable polygonal mirror 201 for deflecting the laser beam and for scanning an image, a lens 203 for collecting the scanning light, and the like, these elements being integrally assembled on a support plate 206.
The scanning light emitted from the light scanning apparatus 205 is reflected by a reflection mirror 207 to be directed to a photosensitive drum 208 as a member to be scanned. The reflection mirror 207 is supported by a body of the image forming apparatus through an adjustment mechanism, whereby the scanning light emitted from the light scanning apparatus 205 can be adjusted to be illuminated in parallel with the photosensitive drum 208.
On the other hand, an image forming apparatus wherein a plurality of light beams are obtained by providing a plurality of light scanning apparatuses as mentioned above is shown in FIG. 13. In FIG. 13, a driving portion 302 is provided for driving two rotatable polygonal mirrors 301 in coaxial with each other. The driving portion comprises two sets of condenser lenses for collecting the respective laser beams and a laser beam unit (not shown) for emitting the laser beams to constitute a scanner unit 303. The scanner unit 303 is fitted into holes of a support plate 304 and fixed thereto.
Further, two reflection mirrors 307, 310 are provided for directing the respective scanning light beams to a photosensitive drum 305. A first scanning light 306 is reflected by a first reflection mirror 307 fixed to a side wall of the apparatus, and then is reflected by a reflection mirror 308 attached to the side wall of the apparatus through an adjustment mechanism to reach the photosensitive drum 305. The adjustment mechanism for the reflection mirror 308 comprises an adjusting means for adjusting the scanning light so that the scanning light scans the photosensitive drum 305 in parallel with a longitudinal direction of the drum 305, an illumination point adjusting means for adjusting the scanning light to position it to a predetermined illumination point, and a light path length adjusting means for correctly focusing the laser beam on the photosensitive drum 305.
On the other hand, a second scanning light 309 is reflected by a second reflection mirror 310, and then is reflected by a reflection mirror 311 having an adjustment mechanism similar to the adjustment mechanism for the reflection mirror 308 to reach the photosensitive drum 305.
However, when the plurality of reflection mirrors are arranged on the side wall of the image recording apparatus as in the above-mentioned conventional case, the following drawbacks will occur:
(1) Since the reflection mirrors are arranged on the side wall of the image forming apparatus, the optical adjustment must be effected during the assembling of the light scanning apparatus or after the assembling of the image forming apparatus, thus affecting the efficiency of the assembling of the apparatuses. Further, during the assembling, the reflection mirrors may be damaged or smeared, thus affecting the efficiency of production of the apparatus.
(2) When the reflection mirrors are attached to the side wall of the image forming apparatus, since the reflection mirrors are affected upon the vibration and/or distortion of the side wall of the image forming apparatus, the scanning light beams could not be scanned correctly on the photosensitive drum.
(3) If the error in accuracy of the optical system provided in the image forming apparatus occurs when the apparatus is in the market, it is impossible to re-adjust the optical system in the market, because there is no means for obtaining information regarding the positions where the plurality of scanning light beams are illuminated on the photosensitive drum, the parallelism between the scanning light beams and the photosensitive drum, and/or the relative difference between the scanning light beams, in the market.